.The expression "Earth centered universe" means that the universe and all the planets orbit the earth, this theory was disproved around 400 years ago.
A galaxy is a large collection of dust gas and billions of stars
Humans know the moon is closer to us the sun is, and that the planets are closer then the stars. We know this, because of their relative movements, the stars create an almost unchanging backdrop, while the planets wander.
Astronomers can measure the distances to objects in space be using the indirect method of triangulation
Parallax is the difference in orientation of an object viewed along 2 different lines of sight, and is measured by the angle of inclination between the 2 lines. Closer objects have a larger Parallax then objects that are farther away, so, parallax can be used for measuring distance.
PARALLAX
In physics, an inverse-square law is any physical law stating that some physical quantity or strength is inversely proportionate to the square of the distance from the source of that physical quantity.
How big &How far